1. Field of the Invention
This invention relates in general to liquid crystal displays, and in particular to the structure of materials and preparation methods for the alignment of liquid crystal material which can be used to form a liquid crystal display (LCD) cell.
2. Description of Related Art
Liquid Crystal (LC) displays are used in various applications, e.g., video screens, Automatic Teller Machines (ATMs), laptop computers, etc. However, the processes and materials used to make LC flat panel displays are limited.
Presently, mechanical rubbing or buffing techniques are used on polyimide films to provide an alignment surface to accept the liquid crystals. Other methods and materials can also create LC alignment layers, e.g., stretching a polymer, a Langmuir-Blodgett film, a grating structure produced by microlithography, oblique angle deposition of SiOx, and polarized UV irradiation of a polymer film. All of these methods are very expensive and time consuming and have not achieved completely satisfactory results. Most processes contain a large number of processing steps, which creates more possibility for error, lower device yields, and increases in fabrication time and device cost.
All mechanical rubbing methods have limitations. Some drawbacks arise from the mechanical contact of a rubbing cloth with the surface of the polyimide film. For example, uneven pressure and the varying directionality of the rubbing contacts with the polymer surface lead to non uniformities in the alignment layer. Further, mechanical rubbing methods introduce contamination on the rubbed surface and therefore require cleaning the surface with detergents or solvents. This contamination is also not suitable for a cleanroom environment and requires a special room within the cleanroom to produce the alignment layer, adding a significant cost to manufacturing.
The mechanical rubbing method has limitations in that it is not applicable with a structured surface and it is difficult to implement multidomain and wide viewing angle technology. Further, if a post spacer is incorporated for maintaining an equal spacing between the two plates, mechanical rubbing will cause a shadow effect.
A controllable non-contact method is preferable over the present methods described above because larger viewing angles can be achieved. Further, LC images, in terms of both retention and creation, would be more uniform across the length and width of the display. Also, mechanical methods are time-consuming and costly.
It can be seen, then, that there is a need for a non-contact method for aligning liquid crystals. It can also be seen that there is a need for a low-cost method for creating liquid crystal displays. It can also be seen, then, that there is a need for a method that uses non-polymeric materials for alignment layers.